[brd6]

Description

Link did not extend AbstractJsonSerializable, so its protected properties were invisible to json_encode. Every other property resource in the library extends that base class; Link was the exception.

The consequence is that a rich text carrying a link serialized as "link": [] instead of "link": {"url": "..."}.

$text = Text::fromContent('Linked');
$text->getText()?->setLink((new Link())->setUrl('https://example.test/a'));

$block = (new ParagraphBlock())->setParagraph(
    (new ParagraphProperty())->setRichText([$text]),
);

$block->toArrayForCreate();
// text.link => []   (before)
// text.link => ['url' => 'https://example.test/a']   (after)

This one-line change makes Link extend AbstractJsonSerializable, which is all that is needed for the existing toArray() machinery to serialize it. Reading is unaffected: Link::fromRawData() already worked, and a round-trip test covers it.

Motivation and context

The empty array is rejected by the Notion API, so creating a block with a linked rich text fails outright:

body failed validation: body.children[0].paragraph.rich_text[0].text.link
should be an object, `null`, or `undefined`, instead was `[]`.

Setting the rich text's href instead looks like a viable workaround, but it is not: the API accepts href on create, returns 200, and then silently discards it. The text arrives unlinked and merged into its adjacent runs, so callers get a success response and no link. Serializing text.link as an object is the only shape that produces a hyperlink.

How has this been tested?

• Added tests/Resource/LinkTest.php covering the serialized shape, the omitted empty type, a linked rich text inside toArrayForCreate(), an unlinked rich text (no link key), and a fromRawData() round-trip.
• Full suite: 241 tests, 1234 assertions, all passing on PHP 8.4.
• phpcs and phpstan clean.
• Verified against the live Notion API: appending a callout whose CTA carries text.link.url returns 200 and the created block comes back with the rich-text runs kept separate and href populated on the linked run. The same payload built with href alone comes back with href: null and the runs merged.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

PR checklist

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING.md document.
• I have added tests to cover my changes.